Coccidia parasites infect a wide range of animal species, especially farm animals where they cause significant economic losses due to mortality, morbidity, lower performance and extra costs associated with treatment and prevention. The most common coccidia belong to the genus Eimeria, which infect birds and mammals. Other common coccidian genera found in farm animals are Cryptosporidium and Isospora. 
Cryptosporidium parvum typically infects the small intestine of neonates of ruminants, and is also human pathogen. In the human population, C. parvum and the genetically closely related species C. hominis are mostly diagnosed in individuals with a compromised immune system, mostly people with AIDS, where they cause profuse, long-lasting watery diarrhea. In immunocompetent people Cryptosporidium causes enteritis and diarrhea which is self-limiting. Nevertheless, severe diarrhea and dehydration may cause serious complications in children and in older persons.
Today, two different approaches for the control of coccidioses are used: 1) vaccination, and 2) administration of coccidiostats and anticoccidials. Vaccination against some Eimeria species is commercially available for use in poultry. Other animals must be treated by anticoccidials covering now all known coccidian species. A problem accompanying the use of these drugs, which were mostly synthesized in 1950s-70s, is the risk of resistancy and the need to rotate treatment programs. Also, residuality of these drugs represents a risk if drugs enter the food chain.
Treatment of cryptosporidial infections is problematic due to the lack of reliable drugs, as well as by the limitations associated with immunotherapy (Harp et Goff, 1995; Jenkins, 2004). People may be treated with paromomycin, and by azithromycin, nitazoxanide or lehrazuril, drugs with a limited efficacy against cryptosporidiosis (Blanshard et al., 1997; Giacometti et al., 1998). In animals, the only registered drug is halofuginone-lactate.
Because of these problems, it is evident that there is a need to find new highly effective anticryptosporidial drugs which should not be toxic to the host and should not leave any residual.